The first generation of hard PVD coatings was
single metal nitrides such as TiN, CrN and ZrN.
They have been commercially exploited since the
middle of the 1980s in cutting applications
(because of their higher hardness compared to high
speed steel and cemented carbide) and for
decorative purposes because of their attractive
appearance: TiN has a distinctive yellow gold color,
CrN looks like silver, ZrN has a white gold color.
Alloyed coatings improve hardness, wear
resistance, toughness and oxidation resistance by
introducing other elements such as C, Al and Cr
into the TiN lattice. The three basic coatings - TiN,
TiCN and TiAlN - currently make up more than
70% of the world's coating market.

Multilayer coatings

Further improvements of the properties of
hard PVD coatings were achieved by the deposition
of multilayer structures. By selecting a suitable
combination of materials for the multilayer
structure it is possible to improve the resistance
against wear, corrosion, oxidation.
Multilayer structure has higher toughness and lower hardness comparable with monoblock
coatings. The “sandwich” structure absorbs the
crack by sublayers, therefore a multilayer coating is
usually preferred for high dynamical load, e.g. for
roughing.

Nanocomposite coatings

Nanocomposite structures represent a new
class of materials, consisting in two or more phases
coexisting in a very low volume, crystals having
dimensions of 3...10 nm. In the case of
nanocristallyne materials the number of atoms in a
crystal grain is comparable, or even less, than the
number of atoms that are in the grain limits. In such
conditions the formation of dislocations is inhibited
by the grain limits, and mechanical deformation
takes place by the mechanism of slipping at the
grain limits, not by dislocation movement, which is
the mechanism of deformation in conventional materials. This leads to a significant increasing of
hardness of nanocristallyne materials and to the
development of superhard materials.
By depositing different kinds of materials, the
components (like Ti, Cr, Al, and Si) are not mixed,
and two phases are created. The nanocrystalline
TiAlN or AlCrN grains become embedded in an
amorphous Si3N4 matrix. Nanocomposite coatings
are commercially available since 2003 and they
have outstanding properties and applications.

DLC and OXI coatings

Diamond Like Coating (DLC) is a metastable
form of amorphous carbon with a high percentage
of cubic sp3 elements. DLC coatings improve the
running-in characteristics of chip removal and
forming tools and play an important role in the
treatment of soft and adhesive materials which
cause built-up edges. Today, DLC coatings are
mainly used in component mass production to
protect against wear and tear through less friction.
Oxide and oxinitride coatings serve to
separate tool/component and workpiece and to
achieve a low affinity between the two, especially
in dry cutting processes where high temperatures
are reached. They offer the following advantages:
high resistance against adhesive wear, abrasive
wear, oxidation, oxygen diffusion (the layer
already is as an oxide);
chemical and thermal isolation and chemical
indifference;
reduced friction even at temperatures of more
than 1000 °C;
fewer built-up edges and less material
interdiffusion in the tribo contact zone.